Because of the dramatic drop in cost of computer semiconductor memory, it is becoming economical and efficient to store image data in computer archival storage and use semiconductor memory as a temporary storage site. For example, in a large hospital hundreds of X-ray film images are made every day. In the past these X-ray films were often stored indefinitely. It has been recognized that computer mass storage of such images is preferable if the image can be reproduced with speed and accuracy. For example, such storage might be on optical or magnetic disks. But, a user must be able to convert the archival record back to film.
It is also desirable to produce hard film copies, or the like of images from CAT scanning and magnetic resonance imaging applications, as well as to produce lithographic and photoengraving plates of images directly from digital data for electronic graphic arts, printing and publishing applications.
In U.S. Pat. No. 4,505,578 to Balasubramanian, a photosensitive medium is disposed to receive scanning radiation from a laser for reproducing a digital image. Either the medium or the laser is mounted on a carriage which is propelled by a falling mass. The falling mass works against a hydraulic cylinder and piston in which hydraulic fluid is displaced from the cylinder. The laser produces a beam for scanning in a line transverse to the direction of motion of the carriage. The apparatus produces a mosaic of image pixels on a photosensitive sheet, the image pixels representing digital data.
There are present efforts devoted to devising image reproducers and recorders which are both faster and more compact without sacrificing the excellent image quality of prior devices. For example, a compact scanner/plotter is described in U.S. Pat. No. 4,024,518 to Boston. A photosensitive film is mounted on a rotatable drum. A scanning head moves on a precision leadscrew so as to scan the film in a helical fashion as the drum rotates. The medium receives an exposure that is a function of the gray levels of the image being recorded. Unfortunately, presently available leadscrews are not accurate enough to avoid misregistration between adjacent lines recorded on the medium, which typically are less than 100 microns wide. Further, most drum-type film recorders are slow, typically taking about five minutes to record an image on a 14 inch by 17 inch sheet of film. It would be desirable to record an image on such a film sheet in about twenty seconds. However, such a recording speed would require a drum speed of about 15,000 rpm, which is not practical.
An object of the present invention is to produce an apparatus for reproducing a digitized image on a light sensitive medium which is both compact, accurate and fast without sacrificing image quality.